1. Field of the Invention
This invention relates to heat exchangers and, more particularly, to heat exchangers utilizing tube-to-header joints.
2. Description of Related Art
Heat exchangers of many types, such as radiators, charge air coolers, oil coolers and the like, suffer limited life as a result of high working stresses at their tube-to-header joints. These stresses are a result of thermal expansion and contraction of the tubes, thermal changes in header length, and variations in internal pressure during operation. Since the tubes are usually rigidly attached to a relatively inflexible header by means of soldering, brazing, welding or the like, the resulting stresses ultimately lead to joint fatigue failure or tube fatigue in the area next to the joint.
In an effort to minimize or eliminate the stresses described above, some heat exchangers have been made with grommeted tube-to-header joints. In such heat exchangers, tube openings in the headers are made to be oversize with respect to the tubes. These openings are fitted with resilient grommets, usually made of high temperature silicone rubber. The grommets have slightly smaller openings than the tubes, so that when the tubes are pushed through the grommets the compression fit provides a leak-free connection of each tube to the header. The heat exchanger assembly involves the tedious handling of numerous small parts (the grommets), and lacks any real bond between the tubes and the headers, relying solely on the compression fit to provide a seal. To achieve the desired compression fit with the grommets, the fit and alignment of the core tubes to the grommeted header openings must be critically maintained through close dimensional tolerances. A major disadvantage of this design is that sealing is dependent on providing and maintaining a compression fit between the grommet, tube, and header.
Heat exchangers have also been made with specially made resilient headers. In such heat exchangers, a rigid metal header with oversized tube openings accepts loosely fitted brass ferrules in each tube opening. The brass ferrules are then bonded to the metal header by molding silicone rubber around each ferrule. The brass ferrules are later soldered to brass heat exchanger tubes.
The disadvantages of specially made resilient headers include the substantial amount of skill and labor required to solder the tubes and headers together. Further, great care must be exercised in the soldering operation to prevent destruction of the silicone bond to the ferrules. Also, the specially molded resilient headers are extremely expensive to produce.
Bearing in mind the problems and deficiencies of the prior art, it is therefore an object of the present invention to provide a method of manufacturing a heat exchanger having long-life properties.
It is another object of the present invention to provide a method of manufacturing a heat exchanger with resilient headers or resilient tube-to-header joints.
It is a further object of the present invention to provide a method of manufacturing a heat exchanger having long-life properties and which is substantially simpler to manufacture.
It is another object of the present invention to provide a method of manufacturing a heat exchanger which requires fewer parts.
It is a further object of the present invention to provide a method of manufacturing a heat exchanger which requires less critical dimensional tolerances.
It is yet another object of the present invention to provide a method of manufacturing a heat exchanger which provides improved joint integrity.
It is still another object of the present invention to provide a method of manufacturing a heat exchanger which is easier to assemble.
It is another object of the present invention to provide a method of manufacturing a heat exchanger which provides a resilient tank to header joint.
It is a further object of the present invention to provide a heat exchanger which includes a resiliently bonded tube-to-header joint.
It is another object of the present invention to provide a heat exchanger which includes a sealing joint using compression and bonding.
It is another object of the present invention to provide a heat exchanger which includes a resilient joint including a bonded grommet.
It is another object of the present invention to provide a heat exchanger which includes a resilient tank to header joint.
Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification.
The above and other objects and advantages, which will be apparent to one of skill in the art, are achieved in the present invention which is directed to, in a first aspect, a method of making a heat exchanger by initially providing a header defining openings. The header openings are adapted to receive a plurality of tubes having outer surfaces. The tubes are inserted into the header openings such that the inner surfaces of the header openings and the outer surfaces of the tubes are adjacent to each other. Then, substantially uncured fluid sealing material is applied to at least the inner surfaces of the header openings such that the inner surfaces of the header openings and the outer surfaces of the tubes are connected by the sealing material. Finally, the method includes curing the sealing material after the tubes are inserted into the header openings, the sealing material provides a flexible, bonded, liquid tight, tube-to-header joint.
Preferably, the sealing material is an elastomer, and is cured by room temperature vulcanization or by ultraviolet light. The sealing material may be a liquid applied to the outer surface of the tubes. The inner surface of the header opening and the outer surface of the tubes frictionally fit in one preferred embodiment.
In another embodiment of the present invention a gap is defined by the inner surfaces of the header openings and the outer surfaces of the tubes, and the fluid sealing material is applied in the gap. In such case, the sealing material is essentially uncompressed after the curing.
The method may further include providing a tank having an inner cavity. The tank may be attached to or integral with the header such that the tubes extend through the header openings and open ends of the tubes communicate with the tank inner cavity.
Another aspect of the present invention relates to a method of making a heat exchanger by initially providing a header having openings. The header openings are adapted to receive a plurality of tubes. Then, the method includes providing a tank having an inner cavity. The tank is attached to the header. Next, the method includes inserting the tubes into the header openings and fixedly attaching the tubes to the header such that the tubes extend through the header openings and the open ends of the tubes communicate with the tank inner cavity. Then, the method includes applying substantially uncured fluid sealing material between the tank and the header defining a joint such that the header and the tank are connected by the sealing material. Finally, the method includes curing the sealing material of the joint such that the sealing material provides a flexible, bonded, liquid tight, header-tank joint. The tubes may be attached to the header by brazing.
A further aspect of the present invention provides a method of making a heat exchanger which initially provides a header defining openings having inner surfaces. The header openings are adapted to receive a plurality of tubes having outer surfaces. The method includes applying substantially uncured fluid sealing material to at least the inner surfaces of the header openings. Then, the method includes curing the sealing material, preferably by room temperature vulcanization or ultraviolet light, before the tubes are inserted into the header openings. The cured sealing material provides elastomeric members bonded to the inner surfaces of the header openings adapted to receive the tubes. Then, the tubes are inserted into the header openings such that the inner surfaces of the header openings and the outer surfaces of the tubes are adjacent to each other and are connected by the elastomeric members to provide a flexible, liquid tight, tube-to-header joint. The elastomeric members may be compressed by the tubes to provide the flexible, liquid tight, tube-to-header joint. The elastomeric member includes an internal dimension which may be defined and formed using a Teflon mandrel. The internal dimension preferably is less than an outer dimension of the tube, thereby providing a compression sealing fit between the elastomeric member and the tube.
Yet another aspect of the present invention provides a method of making a heat exchanger comprising an initial step of providing a header defining openings having an inner surface. The method further includes providing a plurality of grommets which may include cured silicone rubber. The grommets define openings having inner surfaces and are adapted to receive a plurality of tubes. The grommets are adapted to fit into the openings in the header. Then, the method includes inserting the tubes into the grommet openings such that the inner surfaces of the grommet openings and outer surfaces of the tubes are adjacent to each other. Next, the method includes applying substantially un-cured sealing material to at least the inner surfaces of the grommets openings such that the inner surfaces of the openings of the grommets and the outer surfaces of the tubes are connected by the sealing material. Finally, the method includes curing the sealing material after the tubes are inserted into the grommet openings, the sealing material provides a flexible, bonded, liquid tight, tube-to-grommet joint. The grommet may be bonded to the header, or bonded to both the header and the tube outer surface.
A related embodiment of the present invention provides a tank having an inner cavity. The tank defines an opening adapted to receive the tubes. The tank is attached to or integral with the header such that the tubes extend through the grommets and the tank opening. The open ends of the tubes communicate with the tank inner cavity. The outer surfaces of the tubes may be attached to the header to form a flexible tube-to-header joint, or may also be substantially rigidly attached. The tank and the header may be attached by a flexible bond to provide a tank-to-header joint which may include a silicone adhesive and is adapted to accommodate thermal expansion of the tubes.
Another aspect of the present invention relates to a method of making a heat exchanger comprising an initial step of providing a header defining openings having an inner surface. The header openings are adapted to receive a plurality of tubes having outer surfaces. The method further includes providing a structure defining openings. The structure openings have an inner surface and are adapted to receive the plurality of tubes. The structure openings are aligned with the header openings to mutually receive the plurality of tubes. A sealant member, preferably including silicone, having at least one bonding surface is positioned between the structure and the header such that the sealant member is adjacent to the outer surfaces of the tubes. Then, the method includes inserting the tubes into the header openings such that the inner surface of the header openings, the inner surface of the structure openings, and the bonding surface of the sealant member are adjacent to each other. Next, the method includes compressing the sealant member between the structure and the header such that the header and the tubes are connected by the bonding surface of the sealant member. Finally, the method includes curing the sealant member after the tubes are inserted into the header openings, thus, the sealant member provides a flexible, bonded, liquid tight, tube-to-header joint.
In a related aspect of the present invention, the method provides a sealant member which may include a first portion of uncured silicone and a second portion of cured silicone. The first portion is positioned toward the header and the tube outer surface such that the first portion is touching the tube outer surface and the header after the sealant member is compressed. Then, the uncured silicone of the first portion of the sealant member is cured.
A related embodiment provides a plurality of grommets defining openings having inner surfaces and adapted to receive the plurality of tubes. The grommets are adapted to fit into the openings in the header, and the tubes are inserted into the grommets in the header openings. The grommets may be bonded to both the tubes and the header.
A further aspect of the present invention provides a heat exchanger which comprises a plurality of tubes having predetermined dimensions. The tubes include an outer surface and are open at one end. A header structure defines a plurality of openings where the openings are adapted to receive the tubes. A plurality of elastomeric sealing joints preferably including a silicone bonding material, are positioned between the outer surface of the tubes and the header, where the sealing joints are bonded to the outer surface of the tubes and the header.
Yet another aspect of the present invention provides a heat exchanger which comprises a header defining openings having inner surfaces. The header openings are adapted to receive a plurality of tubes, and the tubes are inserted through the header openings. A cured-in-place seal is provided between the tubes and the header. The cured-in-place seal may include an internal dimension smaller than an outer dimension of the tubes to provide a compression sealing fit between the tubes and the cured-in-place seal. The seal is bonded to the header providing an elastomeric compression sealing fit between the tube and the seal. In a related aspect, the internal dimensions of the cured-in-place seal may be formed using a Teflon(trademark) mandrel.
Another aspect of the present invention provides a heat exchanger which comprises a header defining openings. The header openings are adapted to receive a plurality of tubes, and the tubes are inserted through the header openings. The heat exchanger includes a cured-in-place seal preferably including silicone between the tubes and the header. The seal is bonded to the tube, and the seal provides an elastomeric compression sealing fit between the header and the seal.
In a related embodiment of the present invention, the heat exchanger may further comprise a tank being integral with the header.
Yet another aspect of the present invention provides a heat exchanger comprising a plurality of tubes having predetermined dimensions. The tubes include an outer surface and are open at one end. A header structure defines a plurality of openings which receive the tubes. A tank is attached to the header structure. The tank includes openings which are adapted to receive the tubes. A sealing member which may include silicone bonding material bonds the tubes to the header.
In a related embodiment of the present invention, the heat exchanger includes a gap between the header and the tank. The sealing member includes a bond of the silicone bonding material between the tank, the header, and the tubes.
Another aspect of the present invention includes a heat exchanger which comprises a plurality of tubes having predetermined dimensions. The tubes include an outer surface and are open at one end. A header structure defines a plurality of openings. The openings are adapted to receive the tubes. A plurality of elastomeric grommets are positioned circumferentially about the outer surface of the tubes. The grommets have at least one bonding portion of sealing material which may include silicone bonding material, adjacent to the tubes and the header. A plurality of sealing joints are provided which include the sealing material of the grommet bonded to the header and the tube.
A further aspect of the present invention provides a heat exchanger which comprises a plurality of tubes having predetermined dimensions. The tubes include an outer surface being open at one end. A header structure defines a plurality of openings which receive the tubes, and the tubes may be fixedly attached to the header structure by brazing. A tank is positioned above the header structure. The tank and the header structure define a gap between the header structure and the tank. The gap is adapted to receive bonding material which provides a sealing member from curing the bonding material to form a flexible bond between the tank and the header structure.